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Technology: Video takes liquid crystals to the silver screen

作者:秋弩谮    发布时间:2019-03-04 10:16:07    

By BARRY FOX SMALL cinemas could profit from replacing their expensive equipment with an affordable video projector that uses a liquid-crystal display. The LCD projector, which was developed by JVC of Japan, and costs only a few thousand pounds, can produce large colour pictures that are brighter and clearer than video projectors costing up to Pounds sterling 100 000. Previous video projectors using LCDs could not produce a large, high-quality image. The LCD, which looks and works like a slide projector, can fill a screen 3 metres across, making it suitable for audiences of up to 80 people. JVC installed one in a small cinema in Tokyo last May. The company said that the audience liked it well enough to encourage other cinemas to buy it when it goes on sale later this year. The new device can also project videos in Cinemascope. But the main market will be clubs, hotels, lecture theatres and larger venues where the expensive video projectors are used for slick promotional presentations. The cheaper video projectors, costing a few thousand pounds each, use a small cathode-ray tube on which the image is displayed. A lens and mirror project this image onto a screen. There are two basic problems with this technology. First, the farther the screen is from the tube, the dimmer the projected picture becomes. Secondly, slight variations in the Earth’s magnetic field bend the electron beam in the cathode-ray tube and distort the image. These anomalies are not noticeable on a small screen, but are obvious on a large one. Video projectors that produce larger images rely on an expensive technique in which a film of oil acts as a light valve, transmitting and amplifying light as a vacuum valve does a current of electrons. Here, a scanning electron beam forms the image on a film of oil. A bright light shines through this light valve, transmitting and amplifying the image. JVC’s new projector does not use a cathode ray tube or light valve. Instead, it contains three liquid crystal panels, each of which measures about 5 centimetres across the diagonal and contains 210 000 liquid crystal cells. Each panel displays one of the primary colours, red, green or blue, in the image. Each panel is also covered with a light filter of the matching colour. A 250-watt quartz halogen lamp, similar to the lamps used in slide projectors, shines light through the panels. The resulting image is projected through a lens onto a screen. The panels and lens are aligned so that the three colour images superimpose on screen to produce a full-colour picture. As no electron beam is used, the Earth’s magnetic field has no effect. Previous designs of LCD projectors had always produced a mosaic pattern on a large screen because they used only one panel for all three colours. By separating the colours on a panel of 210 000 cells, the images blend together to create a bright picture with little trace of its structure. JVC can also adapt its projector to take Cinemascope videos. This technique produces a squashed image that can be projected on a wide screen. An anamorphic lens is clipped over the projector lens,

 

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